The present invention is intended for use in environments where extremely high degree of filtration is required in a relatively small space. These two requirements tend to conflict and therefore special techniques are required to produce the desired result.
In the computer field for example, there is a need to provide filtration within the sealed enclosures of hard or "Winchester" disk drives. Hard disk drives have an inflexible platter coated with magnetic material which is spun very rapidly. A magnetic read/write head "flies" only a few microns above the disk on an air cushion. If particulate matter were to become lodged between the disk and the head, the disk drive would be destroyed. On the other hand, there is no space for large and sophisticated filtration equipment within the drive since it is a requirement to make the drives as small as possible.
An attempt is made to seal the drive units in a clean environment however particulate matter will always exist or be created by matter breaking away from mechanical structures within the drive and therefore filtration is essential. Ordinary filtration however would create more of a problem than a solution since the filter media itself, at it peripheral edges, is a huge source of particulate matter. The fibers in the media itself are much too large to be allowed to float freely within the enclosure. Therefore, it is essential that the filter not only be capable of trapping existing particulate matter but not contribute to that problem by flaking fibers from its edges.
In the prior art, adhesives have been used to seal the peripheral edges of filter media. This is counter-productive however since the filter assemblies are so small that adhesive seriously reduces the loading capacity of the filter. Remembering that the drive units are sealed for life, there is no opportunity to replace the filter when it is fully loaded.
A second problem existing in prior art devices is the loss of filter capacity resulting from the inability to maintain spacing between the pleats. Existing filter assemblies do not accommodate the accordion type folds of the filter in a manner that maintains uniform distance between adjacent pleats resulting in distortion and significant filter capacity being lost.
The present invention overcomes these problems of fiber flaking and improper pleat spacing while maintaining and maximizing the amount of loading capacity of the filter. Furthermore, this goal is accomplished by a simple and inexpensive assembly structure.